Can't remember what RJJ said about blocking uppercuts during the Khan-Maidiana fight. A tight-high guard doesn't seem logical because fighters can use the chest to guide up to the chin. Maybe someone on NSB would know.

A high guard that is tight enough so that elbows can meet but most fighters have too much bulk to achieve this.

I was always taught to keep a tight guard and lean back, you may still get hit but if your chin is tucked and your leaning back the uppercut gets deflected on forearms (reducing power) and tends to land on the forehead, a much more solid place to be hit with.

But yea, a cross armed defense is best against uppercuts but leaves you pretty wide open for hooks upstairs

holding you strong hand palm down---and then leaning to your strong side afterward--that's how i used to block them---it worked great for me--but everyone's different--find your comfort level when doing it--